1. Field of the Invention
The present invention relates to a dispersant for plaster. In particular, the present invention relates to a dispersant for plaster which can impart proper dispersion to a plaster composition, and has an excellent effect on the foam stability of the composition.
2. Description of the Related Art
Among various dispersants for plaster, such as salts of condensates of naphthalenesulfonic acid with formaldehyde (hereinafter referred to as "the naphthalene compounds"), salts of condensates of melaminesulfonic acid with formaldehyde (hereinafter referred to as "the melamine compounds"), and salts of polycarboxylic acids (hereinafter referred to as "the polycarboxylic acid compounds"). By using these naphthalene compounds, water during mixing step can be reduced and drying time shortened.
In making plaster boards, at first, plaster powder, a dispersant-water mixture, a hardening improver or the like and very fine foam are continuously introduced into a mixer. The mixture is discharged after agitation for about 10 seconds, and is sandwiched by paper boards. But, even if enough foam is introduced, some of the foam breaks which creates undesirable spaces or voids in the plaster board. So, generally twice the amount of foam is introduced. Furthermore, the broken foam concentrates on the faces of the boards which prohibits bonding.